Cross-Slot Bobbin And Antenna Shield For Co-Located Antennas

ABSTRACT

A logging tool includes a mandrel having an axis, a bobbin positioned about the circumference of the mandrel, and defining a first cross slot at a first slot angle and a second cross slot at a second slot angle opposite the first slot angle. The first and second cross slots intersect each other. The tool includes a first antenna in the first slot and including a first plurality of windings wrapped about the mandrel, a second antenna co-located with the first antenna and in the second slot, and an antenna shield secured to the tool mandrel and in each of the first and second slots. The first antenna is arranged in a first orientation and at a first winding angle. The second antenna is arranged in a second orientation and at a second winding angle.

FIELD

The present description relates, in general, to wellbore logging toolsincluding co-located loop antennas and, in particular, to wellborelogging tools including co-located loop antennas disposed in across-slot bobbin for minimizing loss of electromagnetic fields of theco-located loop antennas.

BACKGROUND

During drilling operations for the extraction of hydrocarbons, a varietyof recording and transmission techniques are used to provide or recordreal-time data from the vicinity of a drill bit. Measurements ofsurrounding subterranean formations may be made throughout drillingoperations using downhole measurement and logging tools, such asmeasurement-while-drilling (MWD) tools, which aid in making operationaldecisions, and logging-while-drilling (LWD) tools, which helpcharacterize the formations. LWD tools in particular may obtainmeasurements of the subterranean formations being penetrated bydetermining the electrical resistivity (or its inverse, conductivity) ofthe subterranean formations, where the electrical resistivity indicatesvarious geological features of the formations. These resistivitymeasurements may be taken using one or more antennas coupled to orotherwise associated with the wellbore logging tools.

The wellbore logging tool may include loop antennas each formed frommultiple turns of a conductive wire (or coil) wound on an axial sectionof the wellbore logging tool, such as a drill collar. The wellborelogging tools often are subject to severe mechanical impacts with theborehole wall and with cuttings in the borehole fluid. These impacts maydamage the loop antennas (and other components of the tool) ifunprotected. Antenna shields are commonly used to physically protect theloop antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example drilling system that mayemploy the principles of the present disclosure.

FIG. 2 is a schematic diagram of an example wireline system that mayemploy the principles of the present disclosure.

FIG. 3A schematically illustrates a resistivity logging tool includingtwo co-located loop antennas, according to embodiments disclosed.

FIG. 3B illustrates a dipole electromagnetic (EM) field generated whencurrent is passed through one of the loop antenna of the resistivitylogging tool in FIG. 3A.

FIG. 3C is a graph illustrating the directionality of the dipole EMfield in FIG. 3B in the absence of an antenna shield.

FIG. 3D illustrates a dipole EM field generated when current is passedthrough the other loop antenna of the resistivity logging tool in FIG.3A.

FIG. 3E is a graph illustrating the directionality of the dipole EMfield in FIG. 3D in the absence of an antenna shield.

FIG. 4A illustrates the resistivity logging tool of FIG. 3A including anantenna shield positioned on the co-located loop antennas.

FIG. 4B illustrates the dipole EM field of one of the loop antennas inFIG. 4A in the presence of an antenna shield.

FIG. 4C is a graph illustrating a directionality of the dipole EM fieldin FIG. 4B.

FIG. 4D illustrates the dipole EM field of the other loop antenna inFIG. 4A in the presence of the antenna shield.

FIG. 4E is a graph illustrating a directionality of the dipole EM fieldin FIG. 4D.

FIG. 5A illustrates a cross-slot bobbin positioned about the outercircumference of mandrel of a resistivity logging tool, according toembodiments disclosed.

FIG. 5B illustrates the resistivity logging tool of FIG. 5A includingantenna shields positioned in slots of the cross-slot bobbin, accordingto embodiments disclosed.

FIG. 5C illustrates the dipole EM field generated when current is passedthrough one of the loop antennas of the resistivity logging tool of FIG.5B in the presence of the antenna shield.

FIG. 5D is a graph illustrating the directionality of the dipole EMfield of FIG. 5C.

FIG. 5E illustrates the dipole EM field generated when current is passedthrough the other loop antenna of the resistivity logging tool of FIG.5B in the presence of the antenna shield.

FIG. 5F is a graph illustrating the directionality of the dipole EMfield of FIG. 5E.

FIG. 6 illustrates a cross-sectional view of another cross-slot bobbinpositioned about the outer circumference of the tool mandrel of theresistivity logging tool, according to one or more principles of thepresent disclosure.

FIG. 7 illustrates a cross-sectional view of the cross-slot bobbin ofFIG. 6 having cross slots having different depths, according to one ormore principles of the present disclosure.

In one or more implementations, not all of the depicted components ineach figure may be required, and one or more implementations may includeadditional components not shown in a figure. Variations in thearrangement and type of the components may be made without departingfrom the scope of the subject disclosure. Additional components,different components, or fewer components may be utilized within thescope of the subject disclosure.

DETAILED DESCRIPTION

The present description relates, in general, to wellbore logging toolsused in the oil and gas industry and, more particularly, to wellborelogging tools including co-located loop antennas disposed in across-slot bobbin for minimizing loss of electromagnetic fields of theco-located loop antennas.

The wellbore logging tool, for example, a resistivity logging tool,includes one or more loop antennas at least partially overlapping eachother and each formed by winding multiple turns of a coil about the toolmandrel. This overlapping arrangement of the loop antennas may bereferred to as co-located antennas. Each loop antenna can include anynumber of consecutive “turns” (i.e. windings of coil) about theresistivity logging tool, but typically will include at least aplurality (i.e. two or more) consecutive full turns, with each full turnextending 360° about the resistivity logging tool. Each loop antenna maybe “tilted” or otherwise oriented at an angle relative to thelongitudinal axis of the tool, and the two loop antennas may be haveopposite orientations. In order to minimize cross-talk between theco-located antennas, each loop antenna may be tilted at a loop angle ofabout 45° in opposite directions relative to the tool axis. However, theloop angle is not limited in this regard, and the antennas may bedisposed at a loop angle greater than 0° and less than 90° relative tothe tool axis, without departing from the scope of the disclosure.

The antenna shield is a cylindrical structure that axially spans theportion of the resistivity logging tool including the co-locatedantennas and covers the co-located antennas to protect the co-locatedantennas from mechanical impacts. In order to permit the EM fields topenetrate the antenna shield, and thereby facilitate electromagnetictransmissivity of the antenna shield, a plurality of slots (or openings)may be defined in the body of the antenna shield.

In one or more embodiments, resistivity logging tools include a singleloop antenna wrapped about the mandrel of the resistivity logging tooland tilted relative to the tool axis. An antenna shield may bepositioned radially outward from the loop antenna. The antenna shieldmay cover the loop antenna to provide protection. The antenna shield maydefine a set of longitudinal slots including a plurality of longitudinalslots for permitting EM field to penetrate the antenna shield to betransmitted or received. Each slot may be a through hole in the antennashield that is separated from an angularly adjacent slot. The slots canbe arranged along the radially adjacent loop antenna and overlap theloop antenna and are formed in the antenna shield such that each slotextends perpendicular to the radially adjacent loop antenna at any givenangular location about the circumference of the tool mandrel. The slotstrace the loop antenna. Stated otherwise, the centers of the slots maylie in a plane that is at an angle offset from the tool axis. An antennashield for tilted co-located antennas can include a set of longitudinalslots for each co-located antenna.

During operation of the resistivity logging tool including co-locatedantennas covered by an antenna shield having longitudinal slotsperpendicular to the radially adjacent loop antenna, a portion of the EMfield of one loop antenna may “sneak” out or otherwise leak from thelongitudinal slots of the other loop antenna of the co-located antennas.As a result, the effective EM field angle of the co-located loopantennas may be reduced. For instance, if each loop antenna is disposedhaving a loop angle of about 45°, the effective EM field angle of theco-located antenna would be around 33°. The EM field angle may bereferred to as an “effective” EM field angle since the EM field angle isdifferent from the loop angle (45°, in this case). Because of theleaking of the EM fields, there is cross talk between the co-locatedantennas, and the sensitivity of the resistivity logging tool may bereduced.

Embodiments disclosed are directed to resistivity logging toolsmonitoring surrounding subterranean formations adjacent a drilledwellbore and including co-located loop antennas. Each loop antenna isarranged in a slot of a cross-slot bobbin of the resistivity loggingtools and covered by a corresponding antenna shield that defines aplurality of slots extending perpendicular to the windings of the loopantenna. Because the loop antennas are arranged in slots, the EM fieldof one loop antennas is limited from leaking out of the longitudinalslots of the antenna shield of the other loop antenna. Thus, EM fieldleakage is minimized and gain, sensitivity, and efficiency of the loopantennas is improved. Although embodiments disclosed are discussed withreference to two co-located loop antennas each located in a respectivecross slot in the cross-slot bobbin, the number of co-located loopantennas and number of cross slots is not limited in this regard. Theprinciples of the present disclosure are equally applicable toembodiments including three or more co-located loop antennas and threeor more cross slots, without departing from the scope of the disclosure.

FIG. 1 is a schematic diagram of an example drilling system 100 that mayemploy the principles of the present disclosure, according to one ormore embodiments. As illustrated, the drilling system 100 may include adrilling platform 102 positioned at the surface and a wellbore 104 thatextends from the drilling platform 102 into one or more subterraneanformations 106.

The drilling system 100 may include a derrick 108 supported by thedrilling platform 102 and having a traveling block 110 for raising andlowering a drill string 112. A kelly 114 may support the drill string112 as it is lowered through a rotary table 116. A drill bit 118 may becoupled to the drill string 112 and driven by a downhole motor and/or byrotation of the drill string 112 by the rotary table 116. As the drillbit 118 rotates, it creates the wellbore 104, which penetrates thesubterranean formations 106. A pump 120 may circulate drilling fluidthrough a feed pipe 122 and the kelly 114, downhole through the interiorof drill string 112, through orifices in the drill bit 118, back to thesurface via the annulus defined around drill string 112, and into aretention pit 124. The drilling fluid cools the drill bit 118 duringoperation and transports cuttings from the wellbore 104 into theretention pit 124.

The drilling system 100 may further include a bottom hole assembly (BHA)coupled to the drill string 112 near the drill bit 118. The BHA maycomprise various downhole measurement tools such as, but not limited to,measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools,which may be configured to take downhole measurements of drillingconditions. The MWD and LWD tools may include at least one resistivitylogging tool 126, which may comprise a cross-slot bobbin according toembodiments disclosed.

As the drill bit 118 extends the wellbore 104 through the formations106, the resistivity logging tool 126 may continuously or intermittentlycollect azimuthally-sensitive measurements relating to the resistivityof the formations 106, i.e., how strongly the formations 106 opposes aflow of electric current. The resistivity logging tool 126 and othersensors of the MWD and LWD tools may be communicably coupled to atelemetry module 128 used to transfer measurements and signals from theBHA to a surface receiver (not shown) and/or to receive commands fromthe surface receiver. The telemetry module 128 may encompass any knownmeans of downhole communication including, but not limited to, a mudpulse telemetry system, an acoustic telemetry system, a wiredcommunications system, a wireless communications system, or anycombination thereof. The measurements from the BHA including theresistivity logging tool 126 may be processed downhole and the resultsmay be communicated to the surface receiver. Additionally oralternatively, the measurements may be communicated to the surfacereceiver for processing. In certain embodiments, some or all of themeasurements taken at the resistivity logging tool 126 may also bestored within the resistivity logging tool 126 or the telemetry module128 for later retrieval at the surface upon retracting the drill string112.

At various times during the drilling process, the drill string 112 maybe removed from the wellbore 104, as shown in FIG. 2, to conductmeasurement/logging operations. More particularly, FIG. 2 is a schematicdiagram of an example wireline system 200 that may employ the principlesof the present disclosure, according to one or more embodiments. Likenumerals used in FIGS. 1 and 2 refer to the same components or elementsand, therefore, may not be described again in detail. As illustrated,the wireline system 200 may include a wireline instrument sonde 202 thatmay be suspended in the wellbore 104 on a cable 204. The sonde 202 mayinclude the resistivity logging tool 126 described above, which may becommunicably coupled to the cable 204. The cable 204 may includeconductors for transporting power to the sonde 202 and also facilitatecommunication between the surface and the sonde 202. A logging facility206, shown in FIG. 2 as a truck, may collect measurements from theresistivity logging tool 126, and may include computing and dataacquisition systems 208 for controlling, processing, storing, and/orvisualizing the measurements gathered by the resistivity logging tool126. The computing and data acquisition systems 208 may be communicablycoupled to the resistivity logging tool 126 by way of the cable 204.

Even though FIGS. 1 and 2 depict the systems 100 and 200 includingvertical wellbores, it should be understood by those skilled in the artthat principles of the present disclosure are equally well suited foruse in wellbores having other orientations including horizontalwellbores, deviated wellbores, slanted wellbores or the like.Accordingly, it should be understood by those skilled in the art thatthe use of directional terms such as above, below, upper, lower, upward,downward, uphole, downhole and the like are used in relation to theillustrative embodiments as they are depicted in the figures, the upwarddirection being toward the top of the corresponding figure and thedownward direction being toward the bottom of the corresponding figure,the uphole direction being toward the surface of the well, the downholedirection being toward the toe of the well. Also, even though FIGS. 1and 2 depict an onshore operation, it should be understood by thoseskilled in the art that principles of the present disclosure are equallywell suited for use in offshore operations, wherein a volume of watermay separate the drilling platform 102 and the wellbore 104.

FIG. 3A schematically illustrates a resistivity logging tool 300including two co-located loop antennas 302, 304, according toembodiments disclosed. The resistivity logging tool 300 is depicted asincluding the two co-located loop antennas 302 and 304 positioned abouta tool mandrel 306, such as a drill collar or the like. In one or moreembodiments, e.g. as illustrated, the co-located loop antennas 302 and304 are wrapped about the tool mandrel 306, more particularly, within asaddle 301 defined on the tool mandrel 306. The saddle 301 may comprisea portion of the tool mandrel 306 that exhibits a reduced-diameter ascompared to the remaining portions of the tool mandrel 306.

Each loop antenna 302 and 304 can include any number of consecutive“turns” (i.e. windings of coil) about the tool mandrel 306, buttypically will include at least a plurality (i.e. two or more)consecutive full turns, with each full turn extending 360° about thetool mandrel 306. In some embodiments, a pathway for receiving each loopantenna 302 and 304 may be formed in the saddle 301 and along the outersurface 303 of the tool mandrel 306. For example, one or more grooves orchannels may be defined on the outer surface 303 of the tool mandrel 306to receive and seat a respective loop antenna 302 and 304 308. In otherembodiments and as illustrated, however, the outer surface 303 may besmooth or even. The loop antennas 302 and 304 can be concentric oreccentric relative to a tool axis 310 of the tool mandrel 306.

As illustrated, a portion of the turns or windings of each loop antenna302 and 304 may extend about the tool mandrel 306 at a respectivewinding angle 312 and 314 offset relative to the tool axis 310. Morespecifically, the windings of the loop antennas 302 and 304 on opposingsides of the tool mandrel 306 extend about the outer surface 303 at therespective winding angles 312 and 314. The windings, however, transitionto perpendicular to the tool axis 310 at the top and bottom of the toolmandrel 306, at which point the windings transition back to therespective winding angles 312 and 314 on opposing sides of the toolmandrel 306. Successive windings of the loop antennas 302 and 304 (i.e.,one or more successive revolutions of coils of the antennas) advance ina generally axial direction along at least a portion of the outersurface of the tool mandrel 306 such that loop antennas 302 and 304 eachspans an axial length of the tool mandrel.

In the illustrated embodiment, the each winding angle 312 and 314 isabout 45°. With winding angles 312 and 314 of about 45°, the loopantennas 302 and 304 are substantially perpendicular to each other. Asused herein, the phrase “substantially perpendicular” refers to a 90°relative offset between two components, but also encompasses a +/−10°offset from a truly perpendicular relationship, without departing fromthe scope of the disclosure. In such a configuration, the loop antennas302 and 304 have the least amount of cross-talk between each other.Thus, interference between the loop antennas 302 and 304 issubstantially reduced, even though the loop antennas 302 and 304 areco-located.

FIG. 3B illustrates a dipole electromagnetic (EM) field 316 that may begenerated when current is passed through the loop antenna 302. Thedipole EM field 316 may extend radially outward from the loop antenna302 and orthogonal to the winding direction. FIG. 3C is a graphillustrating the directionality of the dipole EM field 316 in theabsence of an antenna shield. As illustrated, the effective EM fieldangle 319 of the dipole EM field 316 is about 45°, which is close to theideally desired angle of 45°.

FIG. 3D illustrates a dipole EM field 318 that may be generated whencurrent is passed through the loop antenna 304. The dipole EM field 318may extend radially outward from the loop antenna 304 and orthogonal tothe winding direction. FIG. 3E is a graph illustrating thedirectionality of the dipole EM field 318 in the absence of an antennashield. As can be seen, the effective EM field angle 321 of the dipoleEM field 318 is about 45°, which is close to the ideally desired angleof 45°. From FIGS. 3B-3E, it can be understood that the loop antennas302 and 304 have minimal cross-talk between each other.

FIG. 4A illustrates the resistivity logging tool 300 having an antennashield 403 positioned on the loop antennas 302 and 304 (illustrated inphantom). The antenna shield 403 includes a cross-slot shield designthat defines a first set 402 of longitudinal slots 412 and a second set404 of longitudinal slots 414 to facilitate electromagnetictransmissivity of the antenna shield 403 by providing areas whereelectromagnetic (EM) signals can penetrate the antenna shield 403 to bereceived or transmitted. In the illustrated embodiment, each slot 412and 414 is formed in the shape of a rectangle, but could alternativelyexhibit other shapes, without departing from the scope of thedisclosure. Each slot 412, 414 is separated from an angularly adjacentslot 412, 414 by a separation gap. The separation gap may or may not beuniform between all angularly adjacent slots 412 and 414. The slots 412cooperatively form a first discontinuous annular ring that extends aboutthe circumference of the antenna shield 403. Similarly, the slots 414cooperatively form a second discontinuous annular ring that extendsabout the circumference of the antenna shield 403. As illustrated, thelength of the slots 412 and 414 increases in a direction angularly awayfrom the point of intersection (generally indicated by 411) of the loopantennas 302 and 304

The antenna shield 403 provides a circumferential encapsulation of theloop antennas 302 and 304 by extending about the tool axis 310. Morespecifically, the antenna shield 403 is positioned radially outward fromthe loop antennas 302 and 304. As illustrated, the antenna shield 403can axially span the axial length of the saddle 301 (FIG. 3A) and issecured to (or otherwise engages) the tool mandrel 306. In someembodiments, the antenna shield 403 may be designed such that arelatively smooth structural transition is achieved between the antennashield 403 and the outer diameter of the tool mandrel 306 at theopposing axial ends of the antenna shield 403.

In some embodiments, the antenna shield 403 can be formed of anon-conductive and/or non-metallic material, such as fiberglass or apolymer (e.g., polyether ether ketone or “PEEK”). In other embodiments,however, the antenna shield 403 can be made of a conductive and/ormetallic material, such as stainless steel, a nickel-based alloy (e.g.,MONEL®, INCONEL®, etc.), a chromium-based alloy, a copper-based alloy,or any combination thereof.

The longitudinal slots 412 of the first set 402 may be arranged alongand overlapping the radially adjacent loop antenna 302. The longitudinalslots 412 of the second set 404 may be arranged along and overlappingthe radially adjacent loop antenna 304. The longitudinal slots 412, 414are formed in the antenna shield 403 such that each longitudinal slot412, 414 extends substantially perpendicular (indicated by respectiveslot angles 405 and 407) to the corresponding radially adjacent loopantenna 302, 304 at any given angular location about the circumferenceof the tool mandrel 306. Stated otherwise, each slot extendsperpendicular to the winding angle of the radially adjacent loopantenna.

FIG. 4B illustrates the dipole EM field 316 of the loop antenna 302 inthe presence of the antenna shield 403. FIG. 4C is a graph illustratinga directionality of the dipole EM field 316 the presence of the antennashield 403. FIG. 4D illustrates the dipole EM field 318 of the loopantenna 304 due to the presence of the antenna shield 403. FIG. 4E is agraph illustrating a directionality of the dipole EM field 318 in thepresence of the antenna shield 403.

As illustrated, due to the antenna shield 403, the dipole EM fields 316and 318 of the loop antennas 302 and 304, respectively, are distortedand the effective EM field angles 319 and 321 are reduced, compared tothe dipole EM fields 316, 318 and effective EM field angles 319, 321 inFIGS. 3B-3E. The effective EM field angle 319 of the dipole EM field 316is about 33°, which is substantially less than the effective EM fieldangle in FIG. 3C (in the absence of an antenna shield). The effective EMfield angle 321 of the dipole EM field 318 is about 33°, which issubstantially less than the effective EM field angle in FIG. 3E (in theabsence of an antenna shield).

The distortion of the dipole EM field 316 (and 318), and the reductionof the effective EM field angle 319 (and 321) may be due to a portion ofthe EM field from the loop antenna 302 (and 304) radiating from thelongitudinal slot 414 (and 412) of the loop antenna 304 (and 302), inaddition to radiating from its corresponding longitudinal slot 412 (and414). Because of leaking of the EM fields, the effective EM field angles319 and 321 of both loop antennas 302 and 304 are reduced.

In order to minimize leakage of the dipole EM fields of the co-locatedantennas 302 and 304, embodiments disclosed may include the co-locatedloop antennas 302 and 304 disposed in a cross-slot bobbin that may bearranged or otherwise positioned about the tool mandrel 306. As aresult, the co-located loop antennas 302 and 304 are isolated from eachother by the cross-slot bobbin.

FIG. 5A illustrates a cross-slot bobbin 502 positioned about the outercircumference of tool mandrel 506 of resistivity logging tool 500,according to one or more principles of the present disclosure. Theresistivity logging tool 500 may be similar to the resistivity loggingtool 126 (FIGS. 1 and 2) and therefore be used in the systems 100 and200.

As illustrated, the cross-slot bobbin 502 is generally cylindrical body501 that may be disposed or otherwise arranged about the tool mandrel506. The cross-slot bobbin 502 includes a first cross slot 512 disposedin the body 501 at a first slot angle 516 offset relative to the toolaxis 510, and a second cross slot 514 disposed in the body 501 at asecond slot angle 518 offset relative to the tool axis 510 and oppositethe first slot angle 516. Each slot 512 and 514 may be a recess orcavity that is defined in the body 501 of the cross-slot bobbin 502 andextending a certain distance radially inward from the outercircumferential surface of the body 501. The first and second slots 512and 514 may intersect each other. Each slot 512 and 514 may be sized andshaped (or otherwise configured) to receive one of the loop antennas 302and 304.

In an embodiment, and as illustrated, the first and second slot angles516 and 518 may be about 45° (e.g., measured along the center of theslot) similar to the winding angles 312 and 314. However, in otherembodiments, the first and second slot angles 516 and 518 may be anyangle greater 0° and less than 90° that can accommodate loop antennas302 and 304 having winding angles greater 0° and less than 90°.

Each slot 512 and 514 may have a same depth (e.g., measured from theouter circumferential surface of the body 501) and thus the loopantennas 302 and 304 may be disposed having substantially similardiameters. Alternatively, in other embodiments (see FIG. 7), the slots512 and 514 may have different depths with one loop antenna having adifferent diameter than the other loop antenna.

The cross-slot bobbin 502 may structurally comprise a high temperatureplastic, a thermoplastic, a polymer (e.g., polyimide), a ceramic, or anepoxy material, but could alternatively be made of a variety of othernon-magnetic, electrically insulating/non-conductive materials. Thecross-slot bobbin 502 can be fabricated, for example, by additivemanufacturing (i.e., 3D printing), molding, injection molding,machining, or other known manufacturing processes

As illustrated, due to the slots 512 and 514, the cross-slot bobbin 502may include two protrusions 503 and 505 extending radially outward fromthe body 501 of the cross-slot bobbin 502 and disposed radially oppositeeach other between the loop antennas 302 and 304. In an example, and asillustrated, the protrusions 503 and 505 may be wedge-shaped. The firstand second slots 512 and 514 thus substantially isolate the loopantennas 302 and 304 from each other and, as a result, the EM fieldsfrom the loop antennas 302 and 304 are limited from interfering witheach other, and cross-talk between the loop antennas 302 and 304 isminimized. It should be noted that the loop antennas 302 and 304 arecoated or otherwise encapsulated with an insulating material and canthus be overlapping and contacting each other while current is flowingthrough each loop antenna.

FIG. 5B illustrates the resistivity logging tool 500 including antennashields 550 and 552 positioned in the slots 512 and 514 of thecross-slot bobbin 502. The antenna shield 550 may include a plurality oflongitudinal shield slots 556 extending substantially perpendicular tothe radially adjacent loop antenna 302 at any given angular locationabout the circumference of the tool mandrel 506. Similarly, the antennashield 552 may include a plurality of longitudinal shield slots 558extending substantially perpendicular to the radially adjacent loopantenna 304 at any given angular location about the circumference of thetool mandrel 506. In an example, each antenna shield 550 and 552 may becomposed of two curved portions that are arranged in the respectiveslots 512 and 514. Each antenna shield 550 and 552 may thus be disposedat a corresponding shield angle 560 and 562 offset from the tool axis510.

In some embodiments, the antenna shields 550 and 552 can be formed of anon-conductive and/or non-metallic material, such as fiberglass or apolymer (e.g., polyether ether ketone or “PEEK”). In other embodiments,however, the antenna shields 550 and 552 can be made of a conductiveand/or metallic material, such as stainless steel, a nickel-based alloy(e.g., MONEL®, INCONEL®, etc.), a chromium-based alloy, a copper-basedalloy, or any combination thereof.

FIG. 5C illustrates the dipole EM field generated when current is passedthrough loop antenna 302 of the resistivity logging tool 500 in thepresence of the antenna shields 550 and 552. FIG. 5D is a graphillustrating the directionality of the dipole EM field of FIG. 5C. Asillustrated in FIG. 5C, the distortion in the dipole EM field 576(relative to the dipole EM field 316 in FIG. 4B) is substantiallyreduced. As illustrated in FIG. 5D, the effective EM field angle 579 ofthe dipole EM field 576 is about 45°. However, embodiments are notlimited in this regard. In other embodiments, one or more of the firstand second slot angles 516, 518, the winding angles 312, 314, the shieldangles 560, 562, and the orientation of the shield slots 556, 558relative to the corresponding loop antennae 302, 304 may be adjusted toobtain an effective EM field angle 579 of a desired value.

FIG. 5E illustrates the dipole EM field generated when current is passedthrough loop antenna 304 of the resistivity logging tool 500 in thepresence of the antenna shields 550 and 552. FIG. 5F is a graphillustrating the directionality of the dipole EM field of FIG. 5E. Asillustrated in FIG. 5E, the distortion in the dipole EM field 578(relative to the dipole EM field 318 in FIG. 4D) is substantiallyreduced. As illustrated in FIG. 5F, the effective EM field angle 581 ofthe dipole EM field 578 is about 45°. However, embodiments are notlimited in this regard. In other embodiments, one or more of the firstand second slot angles 516, 518, the winding angles 312, 314, the shieldangles 560, 562, and the orientation of the shield slots 556, 558relative to the corresponding loop antennae 302, 304 may be adjusted toobtain an effective EM field angle 581 of a desired value.

FIG. 6 illustrates a cross-sectional view of a cross-slot bobbin 602positioned about the outer circumference of the tool mandrel 506 of theresistivity logging tool 500, according to one or more principles of thepresent disclosure. The resistivity logging tool 500 may be similar tothe resistivity logging tool 126 (FIGS. 1 and 2) and therefore be usedin the systems 100 and 200. The cross-slot bobbin 602 may be similar insome respects to the cross-slot bobbin 502 of FIGS. 5A and 5B and,therefore, may be best understood with reference thereto, where likenumerals represent like element not described again. As illustrated, thecross-slot bobbin 602 includes a first cross slot 612 disposed in thebody 501 at a first slot angle 516 offset relative to the tool axis 510,and a second cross slot 614 disposed in the body 501 at a second slotangle 518 offset relative to the tool axis 510 and opposite the firstslot angle 516. Each slot 612 and 614 may be a recess or cavity that isdefined in the body 501 of the cross-slot bobbin 602 and extending acertain distance radially inward from the outer circumferential surfaceof the body 501. Each slot 612 and 614 may be wedge shaped having angledsidewalls 621 and 623 and a bottom surface 625 (forming the bottom ofthe recess). The first and second slots 612 and 614 may intersect eachother. Each slot 612 and 614 may be sized and shaped (or otherwiseconfigured) to receive one of the loop antennas 302 and 304.

Although not illustrated, antenna shield similar to the antenna shields550 and 552 may be positioned in the slots 612 and 614 of the cross-slotbobbin 602. The antenna shields may be sized and shaped (or otherwiseconfigured) to be received in the slots 612 and 614. Each antenna shieldmay include a plurality of longitudinal shield slots (similar to slots556, 558) extending substantially perpendicular to the radially adjacentloop antenna 302, 304 at any given angular location about thecircumference of the tool mandrel 506.

FIG. 7 illustrates a cross-sectional view of the cross-slot bobbin 602having cross slots 612 and 614 having different depths, according to oneor more principles of the present disclosure. As illustrated, the depth701 of the slot 612 (e.g., measured from the outer circumferentialsurface of the body 501) is greater than the depth 703 of the slot 614.However, in other embodiments the slot 614 may have a depth greater thanthe slot 612. Because of the different depths, the loop antennas 302 and304 are separated radially from each other and thus have differentdiameters. For instance, in FIG. 7, the diameter of the loop antenna 302is less than the diameter of the loop antenna 304. In an embodiment, aninterposer (e.g., a piece of fiber glass or similar) may be disposedbetween the loop antennas 302 and 304 where the loop antennas 302 and304 intersect each other. It will be understood that the cross slots 512and 514 of the cross-slot bobbin 502 may also be off different depths,similar to the cross-slots 612 and 614.

Embodiments disclosed herein include:

Embodiment A

A wellbore logging tool, comprising: a tool mandrel having a tool axis;a bobbin positioned about the circumference of the tool mandrel, whereinthe bobbin defines a first cross slot disposed in the bobbin at a firstslot angle and a second cross slot disposed in the bobbin at a secondslot angle opposite the first slot angle, wherein the first and secondcross slots intersect each other, and the first and second slot anglesare defined with respect to the tool axis; a first loop antennapositioned in the first cross slot and including a first plurality ofwindings wrapped about the tool mandrel, wherein the first loop antennais arranged in a first orientation and wherein portions of the firstplurality of windings are wrapped about the tool mandrel at a firstwinding angle defined with respect to the tool axis; a second loopantenna co-located with the first loop antenna and positioned in thesecond cross slot, wherein the second loop antenna includes a secondplurality of windings wrapped about the tool mandrel, the second loopantenna is arranged in a second orientation opposite the firstorientation, and wherein portions of the second plurality of windingsare wrapped about the tool mandrel at a second winding angle definedwith respect to the tool axis; and an antenna shield secured to the toolmandrel and positioned in each of the first and second cross slots,wherein each antenna shield is positioned radially outward fromcorresponding first and second loop antennas and includes a plurality ofshield slots arranged along the corresponding first and second loopantennas and overlapping the corresponding first and second loopantennas.

Embodiment B

A wellbore logging tool, comprising: a tool mandrel having a tool axis;a bobbin positioned about the circumference of the tool mandrel, whereinthe bobbin defines a first cross slot disposed in the bobbin at a firstslot angle and a second cross slot disposed in the bobbin at a secondslot angle opposite the first slot angle, wherein the first and secondcross slots intersect each other, and the first and second slot anglesare defined with respect to the tool axis; a first loop antennapositioned in the first cross slot and including a first plurality ofwindings wrapped about the tool mandrel, wherein the first loop antennais arranged in a first orientation, wherein portions of the firstplurality of windings are wrapped about the tool mandrel at a firstwinding angle defined with respect to the tool axis, and wherein thefirst winding angle and the first slot angle are same; a second loopantenna co-located with the first loop antenna and positioned in thesecond cross slot, wherein the second loop antenna includes a secondplurality of windings wrapped about the tool mandrel, the second loopantenna is arranged in a second orientation opposite the firstorientation, wherein portions of the second plurality of windings arewrapped about the tool mandrel at a second winding angle defined withrespect to the tool axis, and wherein the second winding angle and thesecond slot angle are same; and an antenna shield secured to the toolmandrel and positioned in each of the first and second cross slots,wherein each antenna shield is positioned radially outward fromcorresponding first and second loop antennas and includes a plurality ofshield slots arranged along the corresponding first and second loopantennas and overlapping the corresponding first and second loopantennas.

Embodiment C

A method, comprising: introducing a wellbore logging tool into awellbore, the wellbore logging tool including: a tool mandrel having atool axis; a bobbin positioned about the circumference of the toolmandrel, wherein the bobbin defines a first cross slot disposed in thebobbin at a first slot angle and a second cross slot disposed in thebobbin at a second slot angle opposite the first slot angle, wherein thefirst and second cross slots intersect each other, and the first andsecond slot angles are defined with respect to the tool axis; a firstloop antenna positioned in the first cross slot and including a firstplurality of windings wrapped about the tool mandrel, wherein the firstloop antenna is arranged in a first orientation and wherein portions ofthe first plurality of windings are wrapped about the tool mandrel at afirst winding angle defined with respect to the tool axis; a second loopantenna co-located with the first loop antenna and positioned in thesecond cross slot, wherein the second loop antenna includes a secondplurality of windings wrapped about the tool mandrel, the second loopantenna is arranged in a second orientation opposite the firstorientation, and wherein portions of the second plurality of windingsare wrapped about the tool mandrel at a second winding angle definedwith respect to the tool axis; and an antenna shield secured to the toolmandrel and positioned in each of the first and second cross slots,wherein each antenna shield is positioned radially outward fromcorresponding first and second loop antennas and includes a plurality ofshield slots arranged along the corresponding first and second loopantennas and overlapping the corresponding first and second loopantennas; and obtaining measurements of a surrounding subterraneanformation with the wellbore logging tool.

Each of embodiments A, B, and C may have one or more of the followingadditional elements in any combination. Element 1: wherein the first andsecond cross slots have a same depth. Element 2: wherein the first andsecond cross slots have different depths. Element 3: wherein the bobbinincludes two protrusions extending radially outward and disposed betweenthe first and second loop antennas opposite each other. Element 4:wherein the first slot angle is same as the second slot angle. Element5: wherein the first and second cross slots are configured such that aneffective field angle of a dipole electromagnetic (EM) field of thefirst loop antenna is about 45°. Element 6: wherein the first and secondcross slots are configured such that an effective field angle of adipole electromagnetic (EM) field of the second loop antenna is about45°. Element 7: wherein the first and second loop antennas areconcentric. Element 8: wherein the first and second loop antennas areeccentric. Element 9: wherein the first winding angle is same as thesecond winding angle. Element 10: wherein the first winding angle andthe second winding angle are 45°. Element 11: wherein the shield slotsof each antenna shield are perpendicular to the radially adjacent loopantenna.

Element 12: wherein the tool mandrel is operatively coupled to a drillstring and introducing the wellbore logging tool into the wellborefurther comprises: extending the wellbore logging tool into the wellboreon the drill string; and drilling a portion of the wellbore with a drillbit secured to a distal end of the drill string. Element 13: whereinintroducing the wellbore logging tool into the wellbore furthercomprises extending the wellbore logging tool into the wellbore onwireline as part of a wireline instrument sonde. Element 14: wherein thefirst and second cross slots are each configured such that an effectivefield angle of a dipole electromagnetic (EM) field of each of the firstand second loop antennas is about 45°. Element 15: wherein the shieldslots of each antenna shield are perpendicular to the radially adjacentloop antenna.

A reference to an element in the singular is not intended to mean oneand only one unless specifically so stated, but rather one or more. Forexample, “a” module may refer to one or more modules. An elementproceeded by “a,” “an,” “the,” or “said” does not, without furtherconstraints, preclude the existence of additional same elements.

Headings and subheadings, if any, are used for convenience only and donot limit the disclosure. The word exemplary is used to mean serving asan example or illustration. To the extent that the term include, have,or the like is used, such term is intended to be inclusive in a mannersimilar to the term comprise as comprise is interpreted when employed asa transitional word in a claim. Relational terms such as first andsecond and the like may be used to distinguish one entity or action fromanother without necessarily requiring or implying any actual suchrelationship or order between such entities or actions.

Phrases such as an aspect, the aspect, another aspect, some aspects, oneor more aspects, an implementation, the implementation, anotherimplementation, some implementations, one or more implementations, anembodiment, the embodiment, another embodiment, some embodiments, one ormore embodiments, a configuration, the configuration, anotherconfiguration, some configurations, one or more configurations, thesubject technology, the disclosure, the present disclosure, othervariations thereof and alike are for convenience and do not imply that adisclosure relating to such phrase(s) is essential to the subjecttechnology or that such disclosure applies to all configurations of thesubject technology. A disclosure relating to such phrase(s) may apply toall configurations, or one or more configurations. A disclosure relatingto such phrase(s) may provide one or more examples. A phrase such as anaspect or some aspects may refer to one or more aspects and vice versa,and this applies similarly to other foregoing phrases.

A phrase “at least one of” preceding a series of items, with the terms“and” or “or” to separate any of the items, modifies the list as awhole, rather than each member of the list. The phrase “at least one of”does not require selection of at least one item; rather, the phraseallows a meaning that includes at least one of any one of the items,and/or at least one of any combination of the items, and/or at least oneof each of the items. By way of example, each of the phrases “at leastone of A, B, and C” or “at least one of A, B, or C” refers to only A,only B, or only C; any combination of A, B, and C; and/or at least oneof each of A, B, and C.

It is understood that the specific order or hierarchy of steps,operations, or processes disclosed is an illustration of exemplaryapproaches. Unless explicitly stated otherwise, it is understood thatthe specific order or hierarchy of steps, operations, or processes maybe performed in different order. Some of the steps, operations, orprocesses may be performed simultaneously. The accompanying methodclaims, if any, present elements of the various steps, operations orprocesses in a sample order, and are not meant to be limited to thespecific order or hierarchy presented. These may be performed in serial,linearly, in parallel or in different order. It should be understoodthat the described instructions, operations, and systems can generallybe integrated together in a single software/hardware product or packagedinto multiple software/hardware products.

In one aspect, a term coupled or the like may refer to being directlycoupled. In another aspect, a term coupled or the like may refer tobeing indirectly coupled.

Terms such as top, bottom, front, rear, side, horizontal, vertical, andthe like refer to an arbitrary frame of reference, rather than to theordinary gravitational frame of reference. Thus, such a term may extendupwardly, downwardly, diagonally, or horizontally in a gravitationalframe of reference.

The disclosure is provided to enable any person skilled in the art topractice the various aspects described herein. In some instances,well-known structures and components are shown in block diagram form inorder to avoid obscuring the concepts of the subject technology. Thedisclosure provides various examples of the subject technology, and thesubject technology is not limited to these examples. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the principles described herein may be applied to otheraspects.

All structural and functional equivalents to the elements of the variousaspects described throughout the disclosure that are known or later cometo be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. § 112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor”.

The title, background, brief description of the drawings, abstract, anddrawings are hereby incorporated into the disclosure and are provided asillustrative examples of the disclosure, not as restrictivedescriptions. It is submitted with the understanding that they will notbe used to limit the scope or meaning of the claims. In addition, in thedetailed description, it can be seen that the description providesillustrative examples and the various features are grouped together invarious implementations for the purpose of streamlining the disclosure.The method of disclosure is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, as the claims reflect,inventive subject matter lies in less than all features of a singledisclosed configuration or operation. The claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparately claimed subject matter.

The claims are not intended to be limited to the aspects describedherein, but are to be accorded the full scope consistent with thelanguage claims and to encompass all legal equivalents. Notwithstanding,none of the claims are intended to embrace subject matter that fails tosatisfy the requirements of the applicable patent law, nor should theybe interpreted in such a way.

What is claimed is:
 1. A wellbore logging tool, comprising: a toolmandrel having a tool axis; a bobbin positioned about the circumferenceof the tool mandrel, wherein the bobbin defines a first cross slotdisposed in the bobbin at a first slot angle and a second cross slotdisposed in the bobbin at a second slot angle opposite the first slotangle, wherein the first and second cross slots intersect each other,and the first and second slot angles are defined with respect to thetool axis; a first loop antenna positioned in the first cross slot andincluding a first plurality of windings wrapped about the tool mandrel,wherein the first loop antenna is arranged in a first orientation andwherein portions of the first plurality of windings are wrapped aboutthe tool mandrel at a first winding angle defined with respect to thetool axis; a second loop antenna co-located with the first loop antennaand positioned in the second cross slot, wherein the second loop antennaincludes a second plurality of windings wrapped about the tool mandrel,the second loop antenna is arranged in a second orientation opposite thefirst orientation, and wherein portions of the second plurality ofwindings are wrapped about the tool mandrel at a second winding angledefined with respect to the tool axis; and an antenna shield secured tothe tool mandrel and positioned in each of the first and second crossslots, wherein each antenna shield is positioned radially outward fromcorresponding first and second loop antennas and includes a plurality ofshield slots arranged along the corresponding first and second loopantennas and overlapping the corresponding first and second loopantennas.
 2. The wellbore logging tool of claim 1, wherein the first andsecond cross slots have a same depth.
 3. The wellbore logging tool ofclaim 1, wherein the first and second cross slots have different depths.4. The wellbore logging tool of claim 1, wherein the bobbin includes twoprotrusions extending radially outward and disposed between the firstand second loop antennas opposite each other.
 5. The wellbore loggingtool of claim 1, wherein the first slot angle is same as the second slotangle.
 6. The wellbore logging tool of claim 1, wherein the first andsecond cross slots are configured such that an effective field angle ofa dipole electromagnetic (EM) field of the first loop antenna is about45°.
 7. The wellbore logging tool of claim 1, wherein the first andsecond cross slots are configured such that an effective field angle ofa dipole electromagnetic (EM) field of the second loop antenna is about45°.
 8. The wellbore logging tool of claim 1, wherein the first andsecond loop antennas are concentric.
 9. The wellbore logging tool ofclaim 1, wherein the first and second loop antennas are eccentric. 10.The wellbore logging tool of claim 1, wherein the first winding angle issame as the second winding angle.
 11. The wellbore logging tool of claim1, wherein the first winding angle and the second winding angle are 45°.12. The wellbore logging tool of claim 1, wherein the shield slots ofeach antenna shield are perpendicular to the radially adjacent loopantenna.
 13. A wellbore logging tool, comprising: a tool mandrel havinga tool axis; a bobbin positioned about the circumference of the toolmandrel, wherein the bobbin defines a first cross slot disposed in thebobbin at a first slot angle and a second cross slot disposed in thebobbin at a second slot angle opposite the first slot angle, wherein thefirst and second cross slots intersect each other, and the first andsecond slot angles are defined with respect to the tool axis; a firstloop antenna positioned in the first cross slot and including a firstplurality of windings wrapped about the tool mandrel, wherein the firstloop antenna is arranged in a first orientation, wherein portions of thefirst plurality of windings are wrapped about the tool mandrel at afirst winding angle defined with respect to the tool axis, and whereinthe first winding angle and the first slot angle are same; a second loopantenna co-located with the first loop antenna and positioned in thesecond cross slot, wherein the second loop antenna includes a secondplurality of windings wrapped about the tool mandrel, the second loopantenna is arranged in a second orientation opposite the firstorientation, wherein portions of the second plurality of windings arewrapped about the tool mandrel at a second winding angle defined withrespect to the tool axis, and wherein the second winding angle and thesecond slot angle are same; and an antenna shield secured to the toolmandrel and positioned in each of the first and second cross slots,wherein each antenna shield is positioned radially outward fromcorresponding first and second loop antennas and includes a plurality ofshield slots arranged along the corresponding first and second loopantennas and overlapping the corresponding first and second loopantennas.
 14. The wellbore logging tool of claim 13, wherein the firstand second cross slots have a same depth.
 15. The wellbore logging toolof claim 13, wherein the first and second cross slots have differentdepths.
 16. The wellbore logging tool of claim 13, wherein the bobbinincludes two protrusions extending radially outward and disposed betweenthe first and second loop antennas opposite each other.
 17. The wellborelogging tool of claim 13, wherein the shield slots of each antennashield are perpendicular to the radially adjacent loop antenna.
 18. Amethod, comprising: introducing a wellbore logging tool into a wellbore,the wellbore logging tool including: a tool mandrel having a tool axis;a bobbin positioned about the circumference of the tool mandrel, whereinthe bobbin defines a first cross slot disposed in the bobbin at a firstslot angle and a second cross slot disposed in the bobbin at a secondslot angle opposite the first slot angle, wherein the first and secondcross slots intersect each other, and the first and second slot anglesare defined with respect to the tool axis; a first loop antennapositioned in the first cross slot and including a first plurality ofwindings wrapped about the tool mandrel, wherein the first loop antennais arranged in a first orientation and wherein portions of the firstplurality of windings are wrapped about the tool mandrel at a firstwinding angle defined with respect to the tool axis; a second loopantenna co-located with the first loop antenna and positioned in thesecond cross slot, wherein the second loop antenna includes a secondplurality of windings wrapped about the tool mandrel, the second loopantenna is arranged in a second orientation opposite the firstorientation, and wherein portions of the second plurality of windingsare wrapped about the tool mandrel at a second winding angle definedwith respect to the tool axis; and an antenna shield secured to the toolmandrel and positioned in each of the first and second cross slots,wherein each antenna shield is positioned radially outward fromcorresponding first and second loop antennas and includes a plurality ofshield slots arranged along the corresponding first and second loopantennas and overlapping the corresponding first and second loopantennas; and obtaining measurements of a surrounding subterraneanformation with the wellbore logging tool.
 19. The method of claim 18,wherein the tool mandrel is operatively coupled to a drill string andintroducing the wellbore logging tool into the wellbore furthercomprises: extending the wellbore logging tool into the wellbore on thedrill string; and drilling a portion of the wellbore with a drill bitsecured to a distal end of the drill string.
 20. The method of claim 18,wherein introducing the wellbore logging tool into the wellbore furthercomprises extending the wellbore logging tool into the wellbore onwireline as part of a wireline instrument sonde.
 21. The method of claim18, wherein the first and second cross slots are each configured suchthat an effective field angle of a dipole electromagnetic (EM) field ofeach of the first and second loop antennas is about 45°.
 22. The methodof claim 18, wherein the shield slots of each antenna shield areperpendicular to the radially adjacent loop antenna.